POOR sleep may be linked to Alzheimer's disease in older adults, according to a new brain imaging study.

The findings follow earlier research indicating that one of the functions of sleep is to purge the brain of toxic proteins.

One such harmful protein is beta-amyloid (Abeta), which accumulates in the brains of people with Alzheimer's.

The new study appears to reinforce the importance of sleep in staving off dementia.

US scientists who looked at data on 70 adults with an average age of 76 found that those who slept less, and who experienced low quality sleep, had higher levels of beta-amyloid.

Self-reported sleep duration in the participants ranged from five to seven hours a night.

The authors, led by Dr Adam Spira, from the Johns Hopkins Bloomberg School of Public Health in Baltimore, wrote in the journal JAMA Neurology: "In summary, our findings in a sample of community-dwelling older adults indicate that reports of shorter sleep duration and poorer sleep quality are associated with a greater Î'beta burden.